The present invention relates to a valve-timing control apparatus for an internal combustion engine, in which opening and closing timings of intake valve and/or exhaust valve of the internal combustion engine are variably controlled.
Japanese Patent Application Publication No. 2008-118779 discloses a previously-proposed valve-timing control apparatus for an internal combustion engine. In this technique, an electric motor is driven in order to improve control responsivity and controllability.
In the above previously-proposed valve-timing control apparatus, a rotation of rotor of a brushless DC motor (electric motor) is transmitted to a cam shaft by using a speed reducer of planetary gear type, and a rotational position of the rotor which has a large number of revolutions per unit time is sensed in order to detect an accurate rotational position of the cam shaft. Particularly, since the rotational position of the cam shaft can be frequently detected even in a low-rotational-speed region of engine such as at the time of engine start, for example, a startability of engine is improved in the cases of a vehicle equipped with idling-stop function and a vehicle of hybrid type.